Ion Mobility-Mass Spectrometry Reveals the Energetics of Intermediates that Guide Polyproline Folding
Ion Mobility-Mass Spectrometry Reveals the Energetics of Intermediates that Guide Polyproline Folding
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DOI：
10.1007/s13361-015-1255-2
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发表时间：
2016-01-01
影响因子：
3.2
通讯作者：
Clemmer, David E.
中科院分区：
文献类型：
--
作者：
Shi, Liuqing;Holliday, Alison E.;Clemmer, David E.
脯氨酸有利于天然蛋白质中的反式构型肽键。虽然顺式/反式配置不同的非天然和非结构化状态，溶剂也影响这些偏好。水诱导聚脯氨酸的全顺式右旋聚脯氨酸-I（PPI）螺旋折叠成全反式左旋聚脯氨酸-II（PPII）螺旋。我们最近的工作表明，这是通过涉及六种解析中间体的顺序机制发生的[Shi，L.，霍利迪，A.E.，施，H.，Zhu，F.，Ewing，MA，拉塞尔，D. H.，Clemmer，D. E.：使用离子迁移率-质谱法表征从PPI到PPII过渡过程中沿着的中间体。J. Am. 136，12702-12711（2014）]。在这里，我们使用离子迁移率-质谱法对折叠中间体进行了第一次详细的热力学测量，这告诉我们这种转变是如何以及为什么发生的。由于肽骨架的水合作用，早期中间体似乎在能量上是有利的，而晚期中间体在热力学上是不利的。然而，折叠仍在继续，因为系统的熵在每个新结构的连续形成时增加。当PPII浸入1-丙醇中时，发生PPII -> PPI转变，但该反应通过非常不同的机制发生。在早期，PPII群体分裂成多个途径，最终通过一个晚期中间体会聚，该中间体继续折叠PPI螺旋。几乎每一步都是吸热的。折叠的结果从一个逐步增加的无序系统，允许一个大规模的搜索一个关键的后期中间。总的来说，这里提供的数据使我们能够建立第一个实验确定的能量表面作为溶液环境的函数的生物聚合物折叠。
Proline favors trans-configured peptide bonds in native proteins. Although cis/trans configurations vary for non-native and unstructured states, solvent also influences these preferences. Water induces the all-cis right-handed polyproline-I (PPI) helix of polyproline to fold into the all-trans left-handed polyproline-II (PPII) helix. Our recent work has shown that this occurs via a sequential mechanism involving six resolved intermediates [Shi, L., Holliday, A.E., Shi, H., Zhu, F., Ewing, M.A., Russell, D.H., Clemmer, D.E.: Characterizing intermediates along the transition from PPI to PPII using ion mobility-mass spectrometry. J. Am. Chem. Soc. 136, 12702-12711 (2014)]. Here, we use ion mobility-mass spectrometry to make the first detailed thermodynamic measurements of the folding intermediates, which inform us about how and why this transition occurs. It appears that early intermediates are energetically favorable because of the hydration of the peptide backbone, whereas late intermediates are enthalpically unfavorable. However, folding continues, as the entropy of the system increases upon successive formation of each new structure. When PPII is immersed in 1-propanol, the PPII -> PPI transition occurs, but this reaction occurs through a very different mechanism. Early on, the PPII population splits onto multiple pathways that eventually converge through a late intermediate that continues on to the folded PPI helix. Nearly every step is endothermic. Folding results from a stepwise increase in the disorder of the system, allowing a wide-scale search for a critical late intermediate. Overall, the data presented here allow us to establish the first experimentally determined energy surface for biopolymer folding as a function of solution environment.